It is known that during the installation of concrete floors, the troweling and finishing operation is performed on the wet concrete using either walk-behind or ride-on power trowels. Inasmuch as at least one type of power trowel machine is generally already on site during the installation of concrete floors, the present invention seeks to use the on-site availability of these machines for surface finishing purposes. As used herein, the term “surface finishing” refers to the desired surface texture on a concrete slab after troweling and final setting of the concrete. In addition, generally, concrete contractors do not have specialty surface processing machines on site for surface finishing and typically do not own such machines. Therefore, where specialty surface processing machines are used to surface finish concrete surfaces, concrete contractors have to invest in and own or lease separate, expensive pieces of equipment. As used herein, the terms “surface processing machines” and “surface processing tools” refers to machines and tools used for surface finishing a concrete slab.
In one of its forms, the present invention takes advantage of the larger finished area attainable with ride-on power trowel machines by converting these power trowel machines to surface processing machines suitable for tasks other than troweling. Ride-on power trowel machines typically range in size from approximately 6 feet to slightly more than 10 feet in width and produce a troweled area of up to 40 square feet. The largest units weigh more than a ton and can finish about 30,000 square feet per day. Ride on trowels, such as the trowel machine illustrated in FIG. 1, can be configured with two or more spider assemblies, each having a plurality of radially oriented, spaced-apart arms and a trowel blade mounted on and below each arm. The blades on adjacent rotors may be overlapping or non-overlapping. A typical four arm spider assembly suitable for use with either a ride-on or walk-behind power trowel is illustrated in FIG. 2. The assembly generally includes four radially extending arms emanating from a central hub, which receives a drive shaft. A trowel blade is mounted directly via bolts or indirectly via a mounting bar on and below each of the arms. Concrete troweling machines having spider assemblies for mounting trowel blades, and the manner of attachment of the trowel blades to the spider arms, are discussed in detail in U.S. Pat. No. 7,059,801—Snyder et al, the disclosure of which is incorporated herein by reference.
Converting walk-behind or ride-on trowel machines to general purpose surface processing machines involves providing mounting means which allows the rapid, on-site substitution of surface processing tools, such as circular brushes, on the spider arms in place of the trowel blades which were used during the installation of the concrete floor. Such mounting means have the advantage that they can mount surface processing tools, instead of blades, such as scrubbing, brushing, buffing, grinding and polishing tools, on the spider arms using readily available hand tools in a very short period of time without need for heavy or expensive equipment. Exemplary currently available mounting means which can accomplish the rapid mounting of rotatable surface processing tools on troweling machines are disclosed in U.S. Pat. No. 7,815,393—Snyder et al, the disclosure of which is incorporated herein by reference. Rotatable surface finishing tools are mounted to each of the spider arms, frequently using a mounting bar, with their rotational axes in vertical registry with and directly beneath the spider arm, such that as the spider arms rotate about the hub, the rotatable surface processing tools, e.g., circular brushes, on each arm are intended to be free to spin about a mounting axis perpendicular to the spider arms and parallel to the axis of rotation of the spider arms. Likewise, non-rotatable finishing tools, e.g., grinding stone holders, are conventionally mounted with their longitudinal axis in vertical registry with and directly beneath the spider arm.
During troweling operations on wet concrete surfaces, the surface is finished or smoothed in steps, starting with a rough finish and stepwise moving toward a so-called burnished finish. In the initial steps the spider arms and, thus, the attached trowel blades, are pivoted or pitched by the operator just a few degrees to slightly raise the leading edge of the blade off the concrete surface in order to avoid its inadvertent digging in to the concrete surface while the weight of the troweling machine maintains the trailing edge of the blade in contact with the concrete. The angle θ formed between the blade 36 and the concrete, as shown in FIG. 3, is referred to as the pitch of the blade. As surface finishing of the wet concrete progresses, the pitch of the blade is increased gradually from slightly above zero pitch to the maximum pitch of the blades, typically about θ=25°-30° in FIG. 3, on successive passes to put increasingly greater pressure on the concrete surface. The terms “leading edge” and “trailing edge” refer to the edges of the trowel blade as a function of the direction of rotation of the spider assembly, i.e., clockwise or counter-clockwise. Correspondingly, the terms “leading side” and “trailing side” refer to the sides of each of the arms 32 of the spider assembly as a function of the direction of rotation of the spider assembly, i.e., clockwise or counter-clockwise. FIGS. 4A, 4B and 4C illustrate an end view of a spider arm 32 when the spider assembly is rotating in a clockwise direction. In this and other figures the arcuate arrow indicates the direction of rotation, i.e. clockwise or counterclockwise, of the spider arm and assembly. Spider arms are typically polygonal in cross section, e.g., square, rectangular, hexagonal, octagonal, etc. FIG. 4B shows the spider arm 32 in a horizontal or unpivoted position. FIG. 4A illustrates a spider arm 32 pivoted into a leading side 32a down position while FIG. 4C shows a spider arm 32 pivoted into a trailing side 32b down position. Without a blade attached to each spider arm 32, but with a surface processing tool attached directly under the spider arm, the spider arms of many conventional troweling machines tend to pivot, more or less, toward a trailing side 32b inclined down position as shown in FIG. 4C. If one compares the pivoted trailing side 32b inclined down position of the spider arm in FIG. 4C with the unpivoted position of the spider arm in FIG. 4B it will be appreciated that the trailing side 32b pivoted down position is the same as the pitched trowel blade trailing edge down position desirable during wet concrete finishing operations using trowel blades. This tendency to pivot to a trailing side down position presents a problem when trowel blades are removed from the spider arms and surface processing tools, such as brushes, grinding stones, grinding pads or other honing or polishing pads are installed on the spider arms. The problem is particularly, but not exclusively, noted when the surface processing tool is a rotating tool and a bearing is mounted between the spider arm and the tool in an effort to allow the tool to freely spin as the spider arm is circularly driven by the trowel assembly motor. This is because a rotating tool bearing is designed to have enough play to allow it to absorb forces encountered during use, such as a brush striking bumps on the floor or impacting with walls, and this play allows the bearing to pivot severely due to the trailing side down pivoting of the spider arm. The result is that the bearing tends to bind and is unable to freely rotate, causing it to wear more rapidly than it would in normal use. At the same time, the attached surface processing tool is unable to freely rotate, is not oriented flat on the concrete surface and is caused, by the spider arm pivoting, to wear unevenly, which shortens the tool's useful life. Similar uneven wear is noted when the surface processing tool is non-rotatable, such as a grinding stone surface processing tool housed within a grinding stone holder, when the holder is mounted on and directly beneath the spider arms.